The Analysis of Total Petroleum Hydrocarbons

Hazel Davidson

Technical Marketing Manager Derwentside Environmental Testing Services

Derwentside Environmental Testing Services

DETS is an independent testing laboratory with over 100 staff. We offer analytical testing on a variety of matrices including :

Soils, water, gases, waste, asbestos and fuels

We offer:

A personal service and designated point of contact

Accreditation to ISO 17025 for most determinands and sampling

Accreditation to MCERTs for soils and waters

Flexible testing protocols

Technical support and training for clients

DETS – dependable data, dependable delivery

DETS – dependable data, dependable delivery

Petroleum Hydrocarbons

Composition of TPH

Common refinery products

Behaviour of TPH in soil

Sampling precautions

VPH/EPH methods

Example chromatograms

TPH forensics

Characteristics of Petroleum Hydrocarbons

Thousands of compounds derived from crude oil

Varying in appearance from pale yellow condensates to black tars, with SG of <1 (0.7 – 0.95)

Toxicity, mobility and environmental persistance of compounds is highly variable

Crude oil: predominantly C + H, plus N, S + O

Properties of Petroleum Products (1)

Generally with increasing molecular size (usually recorded as ‘carbon number’) there is:

increase in boiling and melting points

lower vapour pressure

increase in density

decrease in water solubility

stronger adhesion to soils and therefore

less mobility in subsurface conditions

Oil Fraction C Range Boiling Pt. Sol. in H2O Density % Arom.

Gasoline C4-C10 25-215OC Moderate 0.74 10 - 25

Kerosene C10-C15 160-400OC Moderate/ 0.81 <15

& Jet Fuel Low

Diesel Fuel & C12-C28 160-400OC Low 0.86 15 - 20

Light Fuel Oils

Heavy Fuel Oils C19-C35 315-540OC V. low 0.88 15 - 35

Motor Oils & C20-C44 425-540OC V. low 0.90 < 15

Lube Oils

Bitumen > C 35 > 500oC Insol. 1.0 30 - 50

Properties of Petroleum Products (2)

Behaviour in Soil

B. Pt Density (g/cm3) Solubility (mg/l) oC in water Benzene 80 0.87 1800 Toluene 111 0.87 520 Pentane 36 0.62 40 MTBE 55 0.74 26,000 Octane 126 0.70 < 1 Eicosane nC20 343 solid < 1 Triacontane nC35 450 solid < 1

Behaviour in Soil

Hydrocarbons will break down or be removed by: Sorption Degradation – microbial or chemical Dispersion Volatilisation Advective flow – carried along by groundwater Diffusive flow – movement along a concentration gradient The environment (soil matrix, moisture content, pH, TOM, particle size, etc.) will significantly affect the rate of the above

Behaviour in Soil

Sampling for VPH

Soils Suitable for GRO, chlorinated solvents, TML/TEL

It is good practice to take duplicates for each of the above analyses

Also supply a tub of soil for moisture content

No headspace

Waters Volatile organic compounds as above, including

VFAs and dissolved gases

It is good practice to take duplicates, as above

Minimise aeration and agitation when sampling

No headspace, check by inverting vial

60 g glass jar

40 ml vial with PTFE septum

Sampling for EPH

Extractable organics – e.g. EPH, oils, grease, PAHs

Waters - 1 x 500 ml or 1 litre coloured glass bottle,

either no preservative or acid (H2SO4 or HCl)

Soils – 1 x 250 g glass jar

ALL ORGANIC SAMPLES SHOULD BE STORED IN GLASS VESSELS

AT 5oC

Analysis - Hydrocarbon Groups

PIANO - parafins - isoalkanes - aromatics - naphthenes - olefines

Methods of Analysis

Infra red (IR) – limited use

Gas Chromatography – Flame Ionisation Detector (GC- FID)

GCMS – MTBE, PAHs and biomarkers

TPH - Gas Chromatography

VPH by headspace

EPH by extract analysis

Modified US EPA methods

Detection limits:

Soil : 5 mg/kg

Water : 0.01 mg/l

Volatile Petroleum Hydrocarbons (VPH)

Also known as petrol range organics (PRO) or gasoline range organics (GRO)

Carbon range C5- C10, typically up to 400 compounds

Includes n- and iso-alkanes, e.g. pentane, dimethylpentane, octane; and naphthenes (cycloparaffins)

Includes mono-aromatics, e.g. benzene, toluene, ethyl benzene, and xylenes

Can include methyl tertiary butyl ether (MTBE), but GCMS gives greater certainty of identification

VPH - GCFID

Headspace method Column DB – 1 MS length 10 m, diameter 0.1mm Rapid turnaround Minimal sample handling Inexpensive Detection to 10 ppb Total volatiles (C5- C12) + BTEX + banding

BTEX by GC-FID

Benzene ring

Unleaded Petrol

Extractable Petroleum Hydrocarbons (EPH)

Requires solvent extraction Carbon range C10- C40 with speciation Column DB HP – 1MS length 15 m, diameter 0.25mm Includes aliphatics, aromatics and hetero-compounds Includes internal standards Identification of diesel, kerosene, lube oil, plus

degree of weathering Detection limit :

Soils 5 mg/kg Waters 0.01 mg/l

Over 10 years in progress Round robin trials Samples provided by Shell As received soil is preferable Comparison of solvents Analysis by GCFID, not IR Standard in draft format (80% done)

SCA TPH Working Group

Solvent Extraction

HEXANE/ACETONE DCM/METHANOL

DCM/PENTANE

CYCLOHEXANE

FREON 112

Image by ALcontrol

Laboratories

Solvent comparison

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Hexane / Acetone DCM / Methanol DCM / Pentane Cyclohexane Freon 112

Mineral O il

Aromatics

NSO

Solvent Ratio Polarity Total Extract Mineral Oil Aromatics NSO

Hexane / Acetone 1/1 0.5 15823 1549 5553 8721

DCM / Methanol 10/1 0.48 8625 1613 2923 4089

DCM / Pentane 3/1 0.3 2440 1420 749 271

Cyclohexane - 0.26 1739 617 796 328

Freon 112 - 0.24 1137 261 485 391

Extraction of Waters

Liquid/liquid extraction

Stir bar liquid/liquid

Solid Phase Extraction (SPE)

DNAPLs and LNAPLs

Issues to consider:

Solubility in water – generally low

Dissolved, colloidal, or product layer?

To filter or not to filter?

Identification – Known Sample

– Retention Time

Quantification – Calibration Standards

Banding – Retention Time

Quality – QC

– Blanks

– Duplicates

– Calibration Checks

– Proficiency Testing

Gas Chromatography

Chromatograms

Bio Fuel Sample with possible

PAHs Kerosene

Fuel Oil Diesel & Lube oil Diesel

Polar hydrocarbons

Oxygenated fuels

Non-Petroleum compounds

Biogenic material

Plant oils and waxes

Coal material

Fats

Possible Interferences in

TPH analysis

Cleaned up EPH and Mineral Oil

ISO Definition of mineral oil (drinking water):

Compounds in the range C10- C40 which are not

retained by a silica column, using a non-polar

solvent. Chemically, this consists of aliphatics (n-

alkanes, iso-alkanes and cyclo-alkanes) only.

A ‘cleaned up’ EPH requires a moderately polar

solvent for elution – only the polar NSO compounds

will be retained on the column

Speciation

Breakdown of TPH into narrow carbon band ranges (CWG)

Includes VPH and EPH

Includes aliphatics & aromatics

Used in risk assessment packages such as RBCA

Separation

NON-POLAR

SOLVENT

POLAR

SOLVENT

NSO’S (VERY

POLAR)

A A A

B B B

have more

affinity for solid

phase over

solvent

have more

affinity for

phase A over

solvent

have more

affinity for

solvent than

both phase A

and B

has no affinity for

either solid phase

and will elute with

solvent

has more affinity for

solvent and will

elute with solvent

VERY POLAR

SOLVENT

P.A.H’S (POLAR) MINERAL OIL

(NON-POLAR)

Image by ALcontrol Laboratories

Combined Aliphatic and Aromatic Standard

Aromatic Fraction

Aliphatic Fraction

TPH Screen by Rapid GC (C6 – C 40)

• Advantages

Rapid analysis

VPH & EPH in one run

Lower costs

• Disadvantages

Incomplete resolution of all peaks

Higher detection limits

Suitable for soils only

TPH – Forensics analysis

Four main questions: What is it? What was the source? When did it happen? Who was responsible?

Ageing = weathering + biodegradation

Ageing of petroleum products

Most Affected

C10-C20 n-alkanes

Alkylated aromatics

2 and 3 ring aromatics

Least Affected

C20+ alkanes

Cyclo naphthenes

C4-C6 ring aromatics

Most affected

C35-C10 alkanes

Least affected

Iso-prenoids

Pristane

Phytane

C6-C2 ring aromatics

Diesel – fresh and degraded

Most commonly used ratios:

nC17/Pristane

nC18/Phytane

Pristane/Phytane

Ageing of petroleum products

Images by ALcontrol Laboratories

GCFID Methods Advantages

Covers the full TPH range

Good sensitivity (10 ug/l for components)

Carbon chain speciation

Provides a fingerprint

Identify individual analytes i.e. BTEX

Identifies different products

Identifies degree of weathering

Good recovery efficiency

Disadvantages

Slower, and slightly more expensive

TPH Method Summary

VPH by headspace GC-FID – for gasoline

range organics (C5 – C10)

EPH by GC-FID for diesel and lube oil range

organics (C10 – C40)

Cleaned up EPH to remove polars

Speciated TPHCWG for aliphatic and aromatic

banding (C5 – C44)

TPH screen for VPH and EPH combined (C6 –

C40)

The Analysis of Total Petroleum

Hydrocarbons

Thank you

hazel.davidson@dets.co.uk

www.dets.co.uk